Sucker rod steel



May 5, 1942. P. E. MCKINNEY SUCKER ROD STEEL 2 Sheets-Sheet 1 Filed Feb. 14, 1939 N .n A NQ Patented May 5, 1942 SUCKER ROD STEEL Paul E. McKinney, Bethlehem, Pa., assignor to Bethlehem Steel Company, a corporation of Pennsylvania Application February 14, 1939, Serial N01 256,272

4 Claims.

This invention relates to an improved sucker rod steel and to an improved method of heat I treating sucker rods, particularly rods which are suitable for drilling deep oil wells containing corrosive substances such as hydrogen sulphide. The steel for such sucker rods must have a high corrosion fatigue resistance to withstand the alternating high stresses and the corrosive conditions which are imposed on the sucker rods.

My experience with sucker rods and with sucker rod steel has led me to the conclusion that the presence of residual stresses in the steel is conducive to early failure in the well by corrosion fatigue and that a high ratio of proportional limit to yield point is indicative of the absence of residual stresses. I have found that certain nickel-chromium steels which have been used for sucker rods have a high ratio of proportional limit to yield point in'the normalized condition, whereas in other steels such a high ratio can only be obtained by quenching and tempering or by normalizing and tempering. Eliminating the tempering treatment after normalizing effects a considerable reduction in manufacturing costs. this may be done without lowering the service life of the rod. Thus using these nickel-chromium steels as normalized gives both a saving and maximum quality. v

I have discovered that the addition of vanadium to such nickel-chromium steels. raises the values of the proportional limit and yield point without decreasing the ratio o f-the proportional limit to the yield point. Thus, the same high ratio is maintained in the normalizedcondition with considerably higher values of ,these properties. The tensile strength is not materially increased, and 'the ductility is not substantially decreased. This gives a steel with improved elasticity and sucker rods made from it can withstand higher stresses in corrosive wells. Similarly, when operated at moderate stresses increased service life is obtained.

Figure 1 illustrates stress-strain curves of I, a nickel-chromium sucker rod steel with a high ratio of proportional limit to yield point after normalizing; II, a nickel-chromium-vanadium sucker rod steel with an equally high ratio of proportional limit to yield point after normalizing, but with considerably higher values of these Moreover, my experience has shown that properties; III(a), a nickel-molybdenum sucker I tempered, with a high ratio of proportional limit to yield point.

The table below gives the compositions and mechanical properties of the steels shown in Figure 1.

Steel I Steel II fi fg Carbon "percent" 34 23 21 2i Manganese... d0 60 .68 60 60 Phosphorus. do 015 028 028 028 Sulphur Silicon 18 Nickel. Chromium. Vanadium. Molybden 26 Proportional limit pounds per square 1nch 62,000 75,000 32,000 70,000 Yield point do 65, 000 77,000 62,000 72, 000 Tensile strength... d0 95, 000 100,000 94, 000 88,000 Elongation percent 27 27 27 29 Reduction of area ..do. u 60 00 63 66 Ratio P. L./Y. P 95 .97 51 97 I, therefore, consider that the nickel-chromi um-vanadium steels are especially favorably balanced compositions for sucker rods. The range of compositions I have found to give the beneficial effects described are given below:

Carbon Manganese Silicon Nickel Chromium Vanadium Percent Percent Percent Percent Percent Percent 0.1-.5 0.3-1.2 .0.1.8 0.4-1.2 0.2-.8 0.1-.4

The following is a preferred analysis within this range:

Carbon Manganese Silicon Nickel Chromium Vanadium Percent Percent Percent Percent Percent Percent .28 .65 .20 .95 .45 .18

In normalizing sucker rods it is preferable to use a continuous type furnace in which the sucker rods, placed perpendicular to the length of the furnace, are fed slowly through the furnace from the cool entering end to the hot exit end. The rods rest on skids passing longitudinally through the furnace and are pushed on their way through the furnace by lugs on conveyor chains. As they; are pushed along, the rods tend to roll or turn over. There are several skids so that the sucker rods are supported not only at their ends but also at points along their length. Being thus supported and turning over continuously as they are heated to the normalizing temperature, the sucker rods do not kink or sag,

but come out very straight and do not need to be straightened by stretching as was formerly the practice.

Now, at the exit end of such a furnace there is a region extending inward for about a foot or so from the end, at which the temperature is appreciably lower than the normalizing temperature to which the sucker rods are to be heated prior to air cooling. I have'observed that if the rods-pass through this cooler region at the exit end of the furnace at the same slow rate as they travel through the furnace while they are being heated, they do not attain the optimum structure and properties, and in particular they do not attain the high proportional limit and yield point and high ratio of these values which as described above, is desirable in sucker rods whichare subjected to alternating high stresses and corrosive conditions. That is, if the rods are discharged at the same slow rate as they are fed through, they are not cooled from the proper temperature and the rate of cooling from the effective heat treating temperature, is slower than the rate of air cooling which gives the optimum structure and properties.

Thus, I have discovered that for the optimum structure and properties the sucker rods must be immediately cooled in the outer air from the normalizing temperature without for a considerable interval passing through a lower temperature zone before being cooled in the outer air. The latter treatment might indeed be termed intermediate between normalizing and annealing, and is not the normalizing treatment which I have found to be desirable for sucker rods.

As an important part of this invention, therefore, I have devised a method of discharging the sucker rods which retains the advantageous features of the continuous method of feeding, such as rolling of the rods, etc., which give straight sucker rods, but removes the rods from the furnace at a much faster rate than they are fed through. Thus, the rods are air cooled rapidly enough. from the proper normalizing temperature to give the desired properties. This I accomplish by transferring the rods when they reach the proper normalizing temperature within the furnace onto a much faster moving discharge conveyor which removes them from the furnace into the outer air at the desired fast rate.

The means employed are illustrated in Figures 2 and 3,

Figure 2 is a longitudinal section on the line 2-2 of Figure 3, illustrating a furnace and conitleying system in which my invention can be praciced.

Figure 3 is a sectional view on the line 3-3 in Figure 2.

Numeral I is the furnace as a whole. Numeral 2 is the heating chamber, the-entrance end being at the right and the exit end at the left. Numeral 3 shows the main skids for supporting the sucker rods, the skids being supported by I-beams 4.

Numeral 5 shows the main chain conveyor for slowly feeding the sucker rods through the furnace. Numeral 6 shows the lugs on the chain conveyor which engage the sucker rods 1. Nu- 5 merals B and 9 are sprocket wheels for the main chain conveyor, Ill being the drive shaft for 9 and I I the drive shaft for 8. Numeral I2 is the auxiliary fast moving conveyor for discharging the sucker rods, l3 being the lugs on l2 and M the driven sprocket wheel for 12, and I5 the drive shaft for l2. Numeral I6 is an idler sprocket wheel on shaft 8. Numeral l1 represents collars on shaft 8 for holding the idler sprockets in position. Numeral I8 represents the skids for the auxiliary fast moving conveyor. Numeral I9 is an inclined plate. Numeral 2D is a receiving conveyor. Numerals 2| and 22 are openings at the entrance of the furnace and at the exit end, through which the sucker rods enter and leave the heating chamber. Numerals 23 and 24 are openings in the wall of the furnace to permit passage of the chain conveyors, opening 23 being for the slow moving feeding conveyor 5, and opening 24 for the fast moving discharge conveyor I2.

The sucker rods 1 are slowly fed into the furnace on the slow moving conveyor 5 and are slowly heated to the normalizing temperature which is attained when the rods reach the left end of the conveyor 5. At this point the sucker rods are transferred to the fast moving conveyor l2.which rapidly discharges them from the furnace so that they are cooled rapidly in the outer air from the proper normalizing temperature. Conveyor l2 travels about 30 times as fast as conveyor 5. The relative speed may vary as desired, however, within wide limits, for example, conveyor I2 may travel from times as fastto 60 times as fast as conveyor 5.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. A sucker rod of steel containing carbon between approximately .1% and .6%, nickel between .4% and 1.2%, chromium between .2% and .8%, vanadium between approximately .1% and .4% having a normalized structure.

2. A sucker rod of steel containing carbon bemanganese .65%, silicon 20%, nickel .95%,

chromium .45%, vanadium .18%, having a nor malized structure.

PAUL E. MCKINNEY.

4. A sucker rod of steel containing carbon- .28%, I 

